1. Field of the Invention
The present invention relates to a band controlling technology for use with a communication service in which a plurality of connections share a link without a need to reserve bands.
2. Description of the Related Art
In an ATM (Asynchronous Transfer Mode) switch system, information is stored in fixed length cells and the resultant cells are transmitted. The cells are switched by a hardware switch at a high speed. Thus, in the ATM switch system, services for a variety of media such as sound data, image data, and text data, are integrally accommodated and processed. Thus, it is necessary to develop a technology for preventing bands for different services in the switch system from interfering with each other.
Services that are available at the present time are affected by the traffic characteristics thereof. Service qualities are defined corresponding to individual services. The service qualities are referred to as service classes or QOS (Quality Of Service). As one type of service class, an ABR (Available Bit Rate) service is defined.
In the ABR service, each connection transmits data without the need to reserve a band. A plurality of connections are controlled so that the band of a link is impartially used, the link is not exclusively used by a particular connection, and the cells are not improperly discarded. In other words, when there is only one connection that uses a link, the connection can use all the band of the link. However, when many connections use the link, the transmission rates of the individual connections are automatically lowered.
A real example of a related art reference for accomplishing the band control for the ABR service is shown in FIG. 1. In FIG. 1, a switch 101 and a line demultiplexing portion (DMX) 102 monitor the number of cells stored in a buffer thereof so as to determine whether or not a congestion takes place. When the switch 101 or the DMX 102 detects an occurrence of the congestion, an EFCI (Explicit Forward Congestion Indication) bit in a PT (Payload Type) field of a header of a subscriber cell that passes through a point in which the congestion takes place, is set. The resultant subscriber cell is transmitted to a reception side terminal 103. When the reception side terminal 103 receives a subscriber cell in which the EFCI bit has been set, it sets an explicit backward congestion indication bit (that represents that a congestion takes place) to a control cell that is termed a resource management cell (RM cell) and sends back the RM cell to a transmission side terminal 104. The RM cell is a cell in which the value of the PT field of the header of the RM cell is 110. The transmission side terminal 104 sends the RM cell to the reception side terminal 103 at predetermined intervals. When the reception side terminal 103 receives the RM cell, it sends back the RM cell to the transmission side terminal 104. When the transmission side terminal 104 receives the RM cell in which the explicit backward congestion indication bit has been set, the transmission side terminal 104 automatically decreases the transmission rate of subscriber cells corresponding to a predetermined algorithm. On the other hand, when the explicit backward congestion indication bit is not set, the transmission side terminal 104 automatically increases the transmission rate of the subscriber cells corresponding to a predetermined algorithm.
However, in the above-described end-to-end (reception side terminal to transmission side terminal) band controlling technology using the EFCI bit, it takes a long time to start the transmission rate control after a congestion takes place, due to delays of cells on the transmission lines and delays of processes performed in individual terminals. Thus, cells may be adversely discarded.
The present invention is made from the above-described point of view. An object of the preset invention is to accomplish a proper band control that is not performed by an end-to-end communication and also a band control that can be quickly performed.
The present invention is a band controlling apparatus for use with a communication service having connections for sharing a link without a band reservation and for communicating a fixed length cell including routing information necessary for autonomously switching each connection in a switch system and connection identification information for identifying each connection, comprising a service identification information adding portion for adding service identification information that represents that each connection uses the communication service, to a cell that is input to the switch system and that corresponds to each connection that uses the communication service, and a band controlling portion disposed in the switch system that is adapted for identifying a cell of which the service identification information has been added, so as to control a band of each connection that uses the communication service.
According to the structure of the present invention, a switch system itself can quickly send band control information with respect to a communication service such as an ABR service to a transmission side terminal.
Thus, a band control that is not performed by an end-to-end communication and that has a high accuracy can be accomplished. In addition, the communication quality of the above-described communication services can be improved.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings.